A contrast type autofocus (referred to as a “TVAF” hereinafter) has been conventionally known and configured to move a focus lens so that the sharpness (focus signal) of a signal obtained from an image sensor can become maximum. A lens interchangeable type camera system has also been known in which an image pickup apparatus (camera body), such as a digital still camera and a digital camera, generates a focus signal, and a focus lens is driven in an interchangeable lens that is attached to and detachable from the camera body. It is necessary for the TVAF control in this lens interchangeable type camera system to manage the generating timing of the focus signal and the driving timing of the focus lens.
Patent Literature (“PLT”) 1 discloses a method of setting the driving timing of the focus lens in the TVAF control in this lens interchangeable type camera system. PLT 2 proposes a method of transmitting a busy signal from an interchangeable lens to a camera body when the interchangeable lens cannot communicate or cannot execute a command from the camera body.